1. Field of the Invention
This invention relates to a method and apparatus for measuring cigarette pressure drop.
2. Brief Description of Related Art
The draw resistance of a cigarette, or other smoking article, is a major determinant of the draw characteristic(s) of the cigarette which are experienced by a smoker. The draw resistance of a cigarette refers to the resistance of the tobacco rod, and filter element if present, to air flowing therealong. The draw resistance perceived by a smoker can be measured quantitatively by the pressure drop or difference in static pressure between the two ends of a sample cigarette at a fixed air flow rate of 17.5 ml sec.sup.-1. As used herein, the phrases `cigarette pressure drop` or `pressure drop of a cigarette` mean the measured difference in static pressure between the two ends of the cigarette at the fixed flow rate.
The pressure drop of a ventilated filter cigarette can be measured either with the ventilation holes of the filter element open, i.e. the unbound cigarette pressure drop, or with the ventilation holes closed, i.e. the bound cigarette pressure drop. The bound pressure drop of a filter cigarette can be measured by enclosing the full length of the cigarette in a rubber sleeve, such as in one method which can be carried out on the Filtrona Auto P.D. device. Alternatively, the bound pressure drop can be measured by only enclosing a predetermined length of the filter element of the cigarette which, length includes the ventilation holes. This method can also be carried out on the Filtrona Auto P.D. device. Unbound pressure drop measurements can also be made using the Auto P.D. Device whereby the ventilation holes are left open by the rubber sleeve. Another apparatus, the Filtrona Cigarette Test Station, encloses the filter element and the ventilation holes to provide a bound cigarette pressure drop measurement or, alternatively, the ventilation holes can be left open to provide an unbound cigarette pressure drop measurement. The pressure drop of a cigarette has, until recently, only been determined by measuring each finished cigarette in an individual fashion, known as static measurement. However, in U.S. Pat. No. 4,811,744 to which attention is directed, there was disclosed an apparatus for measuring, in a continuous fashion, the on-line pressure drop across a rod of tobacco fibres. The pressure drop across the rod is measured at that point in the format finger on the cigarette making machine where the rod is compacted to a diameter which is substantially the same as the diameter of the finished cigarette, i.e. an on-line pressure drop measurement is taken. This pressure drop measurement correlates very well with the usual static measurement of the pressure drop along a finished cigarette, at the same tobacco density or tobacco rod weight. As the cigarette is enclosed along its length in the format finger the pressure drop is effectively a bound pressure drop measurement. This device, though, is not effective to give a correlation with the unbound pressure drop of a ventilated cigarette.
This invention has as an object the provision of a method for determining the unbound pressure drop of a ventilated plain or filter-tipped cigarette, which pressure drop is indicative of the draw resistance of a cigarette experienced by a smoker. The unbound pressure drop is of considerable practical importance in the production of cigarettes to a particular unbound pressure drop value or range.
The method of determining the unbound pressure drop of a cigarette according to the invention could be utilised to predict, for theoretical purposes say, the unbound pressure drop of any ventilated filter-tipped or plain cigarette, but is preferably configured to predict continuously the on-line unbound pressure drop of a specific cigarette, i.e. a cigarette having a particular desired level of ventilation.